Lime-fly ash compositions for stabilizing finely divided materials such as soils



United States Patent-f LIME-FLY A-SH COMPGSITIONS- FOR STABILIZING SFINELYDIVIDED=MATERIALS SUCH AS SOILS Jules E: Havelin, Havertowmand:FrankiKahn,

Philadelphia, Pa.

Nov Drawing. Application-August 18, 1951, Serial-No. 245,652

9 7. Claims. (Cl. 106-120) the like which contain fineaggregatein'the form of finely 'vidivided sand or other chemically inert aggregate i havi'ing afineness modulus of 1.7 or above. Repeated experime'nts in the laboratory as well aspractical applications +in'the.field have demonstrated that, within specific ranges Ofzrelative proportions of those ingredientsya mixture having unexpectedly high: early: compressive strength was .:obtained.

Wehave now discovered that unexpected advantages are attained by: mixing lime and fiy ash in controlled'proportions with a timely divided .soil having a fineness modulus less than 1.7. We have further found that, for certain soils of fineness modulus below 1.7, certain optimumrelativeproportions of lime and fly ash give unexpected peaks when soil characteristics relating to durability andbearing power of the soil are plotted against percentage. Forexample,- the plasticity index, shrink- "wage characteristics, water retentivi ty and capillary .po-

tential of uncured samplesaswell as modulus of elasticity, unconfined compressive strength "and resistance'to alter- -.;-nate cycles of freezing and thawing and wetting and drying of "cured specimens vary critically within definite iranges 'for definite soils. T-hese-materials'are of such fineness that theyare outside the class of materials usually referred to as aggregates. The compositions of this invention are extremely useful for many purposes and are found particula'rly'useful in the field of soil stabilization ierbuilding load-supporting surfacessuchas air field 'runways,"roads-highways or the like.

'Certain materials which .have previously been'suggested for other purposes wholly unrelated to-soil stabilization "involve the incorporation of lime with fly ash, as exemplified by "the U. "S.patent to Pefier, No. 1,942,769, issued"January 9, 1934. "Pefiers-compositions do not in- -clude'finelydividecl materials'such as soilsor the' like andare-necessarily'indurated, orrsubjected to the action of heat, in order to cause a chemical interaction between the-lime and the'fiy ash. Such induration ordinarily involves intimate contact with steam, which would be difiicult' if'not impossible to accomplish in; building roads oi-highways; Moreover any process involving iridura- 'tion wouldbe" excessively costly and of no practical merit whatsoever in road or highway building operations.

"Anotherprior patent, issued toJ ones and Swezey (U. S.

Patnt'Nol 2,382,154,"August"14, 1945), discloses a buildping blocker brick comprising lime, lly' ash, and certain" i'aluminosiliciciacid materials such as shales, slatesand f'clays. "However, substantial proportions of lime, on the order of 401% lime,far in excess-of .the proportions of lime in applicants compositions,are included in the Jones 2,698,252 YfPatented IDec. -28, 1.954

and the like. Suchstabilized soils are elie'ctively utilized to form load-supportingbases, by which we mean base courses underhighwaysand roads, and for road shoul- .ders, secondary roads, parking areas, airport runways and the like. Several different compositions are being de veloped for stabilization of roads: and highways, the con- ;structionof which is one'ofthelargest industries in the United States. One soil stabilization composition involves the admixture of bituminous materials such as road oils, tars, emulsions and the likewith the soil. Certain soilshave been stabilizedby'mixing with lime, or with bitumin-hydrated .lime :compositions. Portland cement, has also been employed for soil stabilizationyas well as various other'materials. such as organic resins,

calcium chloride and various proprietary materials. However, ;these materials have :not exhibited. certain advan- 1 finishing. therstabilized mixture.

The. surfacing of-airportrunways has presented 'difiiculties in that the jets of jet propelled airplanesusing the runways are frequently:directed against the runway surface. The surface temperature is almost;-instantly brought to a'valuesutficienttocauserspalling of'concretc and cement-like surfacing materials. On ,theother hand,

bituminous materials such .as .asphaltand oil-treated aggregates are inadequate tsurfacing materials for. airport use slnce the bliUInlI1011S"C0nt6I1t ofthe -surface unmediately burns under-theintense heat of the jet.

eand Swezey. composition, and-this has a profound -etfect -aincreasing:importancepinIconstruction,offiroads; highways The primary object of the invention is to provide -economical compositions for stabilizing soilto convert itto a composition well; suited as-a construction material for use inroads, highways and .the like.

- Another object of thepresent invention .is to. provide stabilized fine mineral material having, high. compressive strength. e Still another objector ,the invention is to provide a stabilized -soil .or -equivalent fine 'ma-terialhaving superior durability, wetting and drying resistance, freezing and thawing ;resistance, .-and weathering ,re-

- sistance.

Ano ther object .is.to provide compositions for convertmg: 80118 which have..high plast1c1ty,excessive shrinkage .and poor drainagecharacteristics tocomposition having low plasticity index and improveddimensional stability and drainage properties.

St1ll anotherobject of the invention is to provide a composition ofxmatter forincorporation into afinely divided inertmaterial with capacity to form'astabilized TITllXtL'lIC having modified and. improved engineering char- :acteristics.

Still another object of the invention -is to'provide a relatively inexpensive solid mixture which, when incorporatedinto finely divided. soil.or equivalent mineral 'having a fineness modulus lessv than 1.7, in the presence of moisture, will form a stabilized mixture having resist- .anceto. intense heat andother radiaclly. modified .and. im-

.further become.,apparent hereinafter.

The foregoing and other objectsare attained in accord- .ance with,-this.invention',,by providinga. mix comprising ..lime,ffly ash, ,and aIfinelyqdivided soil, said .soil having a'fineness. modulus less than 1.7.

.Asused. throughout this ,specification and claims t'h .term lirne is used, to indicate; quicklime, hydrated lime,

..and,slaked lime. The term ..hydrated lime.indicates .a dry powder obtainedby treating quicklime with water 1 enough tosatisfy; its chemical-affinity fonwater under the conditions. of its; hydration. It. consists essentially. of .cal- :cium hydrate or a mixture ,of. calciumhydrate and/0r magnesium oxide and/or-magnesium hydroxide. In the above' definitionquicklime is used to indicate acalcined material the majonportionof whichnis calcium oxide (.or

. calcium .oxidein; natural association with a lesser. amount qofmagnesium oxideycapable ,ofslaking with; water. .The .term ,fislaked lime. is .used' interchangeab y. with .-hydrated lime. Both hydrated lime and slaked lime may be associated with excess water, resulting in a moist or slurried state or condition.

The term fly ash as used in the present specification is intended to indicate the finely divided ash residue produced by the combustion of pulverized coal, which ash is carried off with the gases exhausted from the furnace in which the coal is burned and which is collected from these gases usually by means of suitable precipitation apparatus such as electrical precipitators. The fly ash so obtained is in a finely divided state such that at least about 70% passes through a 200 mesh sieve. The fly ash collected from the exhaust gases is hereinafter referred to as crude fly ash.

The term soil is used throughout this specification and the claims hereof is intended to indicate natural or artificial substantially inorganic materials having a fineness modulus below 1.7. While we designate these materials as inorganic, the presence of minor proportions of organic materials is not excluded, provided the fine material is predominantly inorganic.

By fineness modulus we refer to a standard particle size designation determined by sieve analysis. The standard sieves employed are inch, No. 4 sieve (4760 micron), No. 8 sieve (2380 micron), No. 16 sieve (1190 micron), No. 30 sieve (590 micron), No. 50 sieve (297 micron), and No. 100 sieve (149 micron). Fineness modulus of a material is determined by adding the total percentages retained on each of the specified sieves and dividing the sum by 100.

Our invention embraces a wide variety of naturally occurring soils which have a fineness modulus below 1.7. Such soils are well classified in accordance with the Public Roads Administration classification into seven groups identified as Group Al through A7, with subgrouping under A-1, A2 and A4. The principal groups covered in accordance with this invention, and as defined in Bulletin 39 of the Commonwealth of Pennsylvania Department of Highways, June 1948, are Groups A4 through A7, and A2-4 through A-27, as well as certain A3 soils having fineness modulus below 1.7. Group A4 soils are non-plastic or moderately plastic silty soils usually having a high percentage passing the No. 200 sieve. The group includes also mixtures of fine silty soil and up to 64% sand and gravel retained on the No. 200 sieve. These soils ordinarily contain small amounts of colloidal clay. In performance as sub-grade material, Group A4 soils of themselves are subject to objection in that they are, difficult to compact, are subject to frost heaving, and have undesirable elasticity (or poor compressibility) and volumetric shrinkage characteristics.

Group AS soils are micaceous and diatomaceous materials. are finely divided, and are subject to the principal objections noted above in connection with A4 soils.

They are particularly objectionable as sub-grade materials by reason of their elasticity and instability.

Group A6 soils are essentially plastic clay soils usually having 75% or more passing the No. 200 sieve. Similarly Group A-7 soils are clayey materials and exhibit undesirable elasticity as well as volumetric shrinkage. A6 and A7 soils are generally regarded as poor subgrade materials for road and highway construction. The aforementioned Bulletin 39, on page 9 thereof, indicates that the A4. A-S, A6, and A-7 soils are silty and clavey. all being characterized by the fact that at least 36% by weight of the soil passes a standard No. 200 sieve.

Subroups A24 and A-2-5 include gravels or coarse sands having fineness moduli above 1.7 but also include fi e sands havi g fineness moduli below 1.7 which are effectively stabilized in accordance with this invention. The aforementioned Bulletin 39, on pages 7 and 9 thereof indicates th t the A24 and A-2-5 soils are gravels or sands containing a plastic compone t of clay or silt, and that the A2- s ils are characterized by the f ct that a maximum f 35% by weight passes a standard No. 200 sieve. and th t portion of the soil whi h passes a standard No. 40 sieve has a maximum liquid limit of and has a maximum plasticity index of 10. The same bulletin simil rlv identifies A2-5 soils, with the exception that the m nimum liquid limit of the fraction passing a standard No. 40 sieve is 41. Subroups A-2-6 and A-2-7 contain sand and gravel together with a clayey binder component and many of these soils have fineness moduli below 1.7 and are advantageously treated i WCQIdflIIQ? with this invention. On page 9, the aforementioned Bulletin 39 specifies that A-26 and A-2-7 soils are characterized by the fact that they are silty and clayey, and that portion of the soil passing a standard No. 40 sieve has a minimum plasticity index of ll. A3 soils are essentially very fine sands, and those A3 soils having fineness moduli below 1.7 are within the scope of this invention. Natural A3 soils, though occasionally considered satisfactory as sub-grade materials in confined spaces, are generally too mobile or lacking in cementitious materials for average use. The aforementioned Bulletin 39, on pages 7 and 9 thereof, indicates that A3 soils are fine sands having no binder content, at least 51% by weight passing a standard No. 40 sieve, and a maximum of 10% by weight passing a standard N0. 200 sieve.

Finely divided materials other than natural soils, which are equivalent to the soils falling within the above defined soil classifications, nevertheless are included within the scope of this invention. These materials include fine sand, stone screenings, slags, gravel screenings, mineral deposits, fine screenings from quarry operations and the like, having fineness modulus below 1.7, as well as other similar soil-like materials all of which are included within the meaning of the term soils as used herein.

The relative proportions of the three principal components of the compositions are important, in that a wholly unexpected peak is attained, when certain soil characteristics are plotted against the relative proportions of fly ash and lime in the mix, such peak being of the same general character as that represented in Fig. 2 of our aforementioned copending application. Moreover, optimum results are attained for soils of different types by providing lime-fly ash compositions within critical ranges of different scopes. Thus, while the lime, fly ash and soil of our composition may advantageously be present in amounts by weight within the ranges of about lime 2-9, fly ash about 10-30 and soil about 70-90, very advantageous results are attained in different ranges for different soils, as indicated in the following table:

Optimum proportions Parts By Weight Soil Class Lime Fly Ash Soil In the ranges shown above, very advantageous results are obtained, with pronounced optimums occurring particularly with respect to the relative percentages of fly ash. Preferably the parts fly ash and soil, as expressed above, total 100.

The advantages and characteristics of these compositions are readily determined by testing samples thereof for plasticity index, resistance to penetration by standard needle, shrinkage characteristics, water retentivity and capillary potential, for example, such characteristics belng measurable immediately after the mixture is formed. The stabilized soil mixes which show optimum performance as tested by the above characteristics are found to have the most advantageous properties upon aging or curing as reflected by tests for modulus of elasticity, freezing and thawing resistance, wetting and drying resistance, and unconfined compressive strength.

The plasticity index of soil is conventionally defined as the numerical difference between the liquid limit and the plastic limit of a soil. It indicates the range of moisture content in which the soil is in the plastic, or semisolid state. The liquid limit is conventionally defined as the water content at which the soil passes fromxthe plastic state to the liquid state, while the plastic limlt of a soil is the lowest water content at which the 8011 becomes plastic, or the content at which a soil changes from a solid state to a semi-solid state. These tests may be carried out in accordance with AASHO Designations T-89-49, T90 49, and T-9l-49.

The volumetric shrinkage of a soil is tested by meas- -in weight is recorded'as an indication of the auring'the volume-loss of a soilwsar'nple ow-drying, and may"be determined in accordance "with AASHO' Designation T-92-42.

I The water :retentivity of a soil is its abilityrt-ohold water, andmayz'be :determined by applying standardsuc- 'tion to a soil :sample' of standard size,: and measuring mined by placing a wet soil sample of definite size in the top of a funnel the stem or which contains water.

"The open bottom of 'the stem is submerged in a mercury reservoir. Waterispermitted to evaporate from the soil surface, the heightof the mercury column thus drawn up is measured. Capillary potential is usually expressed in termsof feet of water.

Another important characteristic of stabilized soil, which is measurable after a curing or aging period, is its modulus of elasticity, which isoften determined by a conventional dynamic method based upon resonance. The test for modulus of elasticity, or ratio of stress to strain, is of particular importance because many of the other important 'characteristicsof stabilized soil are related to its modulus of elasticity.

The aged or cured stabilized soil specimens may .also he tested for capacity to resist alternate cycles of freezing and thawing and/or wetting and drying. The specimen is subjected to successive cycles and the condition of the specimen is observed at the end of each cycle. After each cycle the surface of the specimen is brushed with a wire brush to' remove loose particles. The loss durability and quality of the soil'composition.

Another important .test which constitutes a definite factor, specifically relatingto the .proportionsof our .materials, is the test .for unconfined compressive strength. Unconfined compressive strength is measured on unconfined cured and dried samples. using conventional testing equipment such as that used for mortars, concrete, and the like. This test conveniently demonstrates the improvement in bearing capacity which is developed by the use-of this invention as contrasted with the very low,

and in many instances negligible bearing capacity of untreated soil expressed in terms of unconfined compressive strength. In fact, the superior strength developed "by this invention improves it"beyond the range measurable by the conventional test which involves measurement of deflection under load.

Ingredients of our-compositions maybe prepared in any conventional manner, such as by simple mixing of the solid components, preferably in the presence of water. However the mixing is preferably carried into efiect by breaking up the soil and mixing the soil with lime and fly ash in predetermined proportions, utilizing suitable soil-breaking and mixing equipment such as that conventionally used for farm and construction purposes, with water added to the mixture in an amount substantially equal to that proportion of water known and defined as the optimum moisture content. Optimum moisture content is determined by the well known modified Proctor test.

Optimum moisture content of asoil or stabilized soil mixture is that'rnoisture content at which the soil-moisture mix has the maximum dry density, or maximum dry weight of solids per unit volume. In practice, the optimum water content varies with each particular soil and stabilized soil mixture, ordinarily within the range of 8-25% moisture'by weight, based on the total dry weight of lime, fly ash, andsoil. Preferably, in incorporating moisture into our stabilized soil mixes, the water content should be controlled within the range of 70%I30% of the optimum water content. Thus the waterfcontent of the stabilized road base may vary from'about 5%-32% by weight,based on the weight of total lime,-.fl y ash, and soil, for difierent soils.

After mixing, the soil. maybe formed tothe desired shape, which may be of any desired character. After curing for several weeks it will develop considerable compressive strength,.but-the cementitious bond of the .mix develops so slowly that even after a.-:week; the

formed mix can readily .be deformed and. re-shaped.

. The following examples are illustrative xofz'the .invenstion:

.2 1". Example A soil was selected comprising a clayey sand, fineness modulus below 1.7, secured from the southern part ofi.Maryland, havingaa relatively high plasticity index of 11.4%. Its Highway Research Board classification was A'2*6. The soil was mixed withlime, fly ash and optimum waterg-itheproportions of-solids beingwasifollowsz .prfiperties-i as ..contrasted. :to th0se.,.of. thewnatural A26 so Thegplasticity index oftltli4%..tor -the natural soil was reduced to 3.5% ,for- .the stabilized soil.

The water retentivity of 8.4 seconds for thewnatural soil was reduced tov 1.5..secondsfor.thestabilized soil.

.The resistance to penetration was increased. A standard ,needlerpenetrated the natural soil a depth of .07 mm., while under, the same. test... conditions-.i.t p netrated the stabilized soil to a depth of only .025 mm.

Specimens were prepare'd'from the'abovern'ixture utilizing moisture at. optimum moisturewcontentaaud compacted and curedfor 28 days. hesespeeimens showed .an unconfined compressive strength of 300 p. s. i. as contrasted to 20 p. s. i. for the natural soil. Resistance to freezing and thawing and wetting and, drying wasalso radically improved as indicated' by. a-standard;';wire' brush test whichshowed that-thestabilized-material-stands up after numerous cycles as contrasted to the native soil which failsrto stand.up:for one cycle.

Highway Research Board classification: A-7. Proportions ofv mixture:

' t a ;v A-7 soil The resulting material at once showed the followin'g properties as constrasted to those of the natural A-7 soil: The plasticity index-.of.-.3.8-.5 %-for the natural soil was reduced to 4..0,%; for-the stabilized soil.

The volumetric shrinkage of 89% "for the naturalsoil was reduced to 15% for the stabilizedsoil.

The capillary potential of 17 feet for thenatural soil wasreduced to 10.2 feet for the stabilized soil.

Specim'ensof the above mixture, combined with opti' mum water and :compacted and cured,for 28 days, showed an unconfined compressive strength of 2000 p. s. i. as contrasted 10.700 p. s. i. for the natural soil, and a resistance ato alternate cycles .offreezing andthawingand wetting and drying for numerous cycles'ascontrasted-to the natural soilj'which failed in the first cycle.

The dynamic :modulus of the cured specimen expressed as the product of the weight of the specimen times the square of the-naturalfrequency was 5 .l'X 10 pounds/sec? while that of" the natural soil was below 0.l l'0 pounds/seek Example 3 Separate samples were compounded with varying proportions by weight of ;lin1e, .fly ash, and A-2-6 soils as follows:

Lime m ash E5 1 10 so 10 99 10 9O 20 20 so 1380 In-the stabilized "soil samples as a'bove prepared, the

7 engineering characteristics of the soil were improved as follows, the range being a function of the composition:

g glf Stabilized Soil Plasticity Index 11.4% o-s.5%.

Compressive Strength (28 days)... 85 p. s. L... 200-300 p. s. 1. Water retentivity 8.4 see 1.5 1se)e. (all samp es Penetration .07 mm .025.03 mm. Dynamic Modulus 2.04.8 10 Less than 0.1X10

lbs/see. lbs./sec.

Example 4 Separate samples were prepared in the manner described in Example 3, using an A-7 soil of fineness modulus below 1.7. The soil was effectively stabilized by the action of lime and fly ash, in proportions by weight natural soil and stabilized soils were as follows:

Natural Soil Stabilized Soil Plasticity Index 38.5% 1-12%. Uneonfined compressive strength 700 p. s. i 1,8502,000 p. s. 1. (28 days). Volumetric shrinkage. l2.515%. Capillary potential 10.26.l feet.

A corresponding mixture was prepared comprising 90 parts of same A-7 soil, 10 parts fiy ash, and 9 parts Portland cement. The plasticity index of this corresponding mixture was 28; thus the incorporation of Portland cement into the soil reduced the plasticity index from 38.5 only to 28, a value which is still considered unsatisfactory.

Example -Various samples were prepared and tested as in Examples 3 and 4, using an A-3 soil having a fineness modulus below 1.7. The proportions of ingredients by weight were as follows:

Lime Fly Ash g 10 9o 10 90 s5 15 85 so 2e 80 The resulting compositions show compressive strengths in the range of 400600 p. s. i. after aging for 28 days, a marked improvement over the natural soil. The stabilized soils also showed ability satisfactorily to resist 12 cycles of alternate freezing and thawing or wetting and drying, whilethe sandy A-3 soil alone fails in the first cycle.

Example 6 An A-3 soil similar to that of Example 5 was stabilized by the formation of a mix consisting essentially by weight of 3 parts lime, 16 parts fly ash, and 84 parts A-3 soil. This stabilized soil had a compressive strength after aging 28 days of 450 p. s. i., and resisted 12 cycles of wetting and drying with a 3.5% weight loss on surface brushmg.

The stabilized soil had a 7-day compressive strength of 1770 p. s. i., as compared to 175 p. s. i. for the natural S01 The following examples represent specific combinations of particular advantage in connection with soils of different types. All the following examples represent highly useful stabilized soils having improved properties for highway construction as compared to the soil prior to stabilization.

Example 8 Parts by weight A-4 soil 84 Lime 3 Fly ash 16 Example 9 A-5 soil 85 Lime 6 Fly ash 15 Example 10 A-6 soil 88 Lime 8 Fly ash 12 Example 11 A-3 soil 88 Lime 2 Fly ash 12 Example 12 A-3 soil 70 Lime 2 Fly ash 30 Example 13 The following example illustrates advantageous compositions in accordance with this invention wherein the finely divided material is an artificial material equivalent to natural soil, and herein defined as soil, parts being by weight:

Proportions Fly Material Lime Ash Sand Crushed limestone screenings (through 10 mesh, fineness modulus 1.5)

Pulverized blast furnace slag (fineness modulus 1.6)

Crushed trap rock (fineness modulus 1.5)

All of the foregoing compositions of Example l3 have compressive strengths in the range of 4006i)0 p. s. i. after aging for 28 days, and show ability to resist about 12 cycles of alternate freezing and thawing or wetting and drying in accordance with conventional tests.

From the foregoing description and examples it will be appreciated that our lime-fly ash-soil compositions are novel generallyand applicable to a wide variety of uses. They are of great advantage by reason of their relatively low cost, engineering properties and strength characteristics. The stabilized, uncured soil product is particularly advantageous in that considerable time (on the order of a week or more) elapses before the mixture sets up more or less completely. During this period the mix is readily handled, spread and compacted, and yet due to the immediate changes in soil properties which are produced, the compacted mixture has a surprisingly great loadbearing capacity during this period, even before complete setting. In our experience the load-bearing characteristic of this newly formed composition has been sufficient to permit the use of a road or highway, for example, before setting is complete. the addition of the lime and fly ash, in the proportions disclosed, immediately converts a natural soil which is relatively poor as a load supporting base to a composition having structural characteristics ideally suited for the purpose.

The property of our compositions to set slowly is of prime importance in road and highway construction, in that constructions schedules need not necessarily be ad hered to rigidly. Moreover, work may be discontinued or postponed due to rain and resumed at a later date without harm to the stabilized soil due to setting or erosion during the interventing period. By contrast, soils stabilized with Portland cement set up rapidly under such conditions.

Another advantage of our stabilized lime-fly ash-soil compositions is that they may be recompacted after several weeks, while soils treated with Portland cement are found to set up quickly and can not satisfactorily be recompacted several weeks after they are first compacted. Our material is also an ideal patching material, which is an additional advantage over Portland cement.

While lime alone or fly ash alone, when mixed with soil, may in certain cases improve certain characteristics of a soil, for use as a load-supporting base, the combination of lime with fly ash produces radically changed characteristics far beyond any results that might be predicted from the behavior of lime alone, or of fly ash alone. The beneficial effects achieved are far in excess of the sum of those attributable to the presence of either lime or fly ash.

Additional materials such as Portland cement, special grades of clay soils and alumino silicates and the like may be incorporated into soil stabilized in accordance with our invention without detrimental eflect to certain of the advantages of the invention. However, the novel stabilized soil road bases themselves consist essentially of the ingredients set forth in the appended claims.

The above description and examples are presented as illustrations of preferred embodiments of the invention. All modifications and variations which conform to the spirit of the invention, including the substitution of equivalents and other changes in the particular form of the method and product, as well as the use of certain advantageous features of the invention without the use of other features, are within the scope of the invention as defined in the appended claims.

Having thus defined our invention, we claim:

1. A stabilized soil composition of matter consisting essentially by weight of about to about 30% inclusive of crude fly ash, about 70% to about 90% inclusive of soil having a fineness modulus below 1.7, the sum of the percentages of crude fly ash plus soil being substantially equal to 100, and about 2% to about 9% inclusive of lime, the percent lime being based on the weight of crude fiy ash plus soil.

2. A stabilized soil composition of matter consisting essentially by weight of about to about 30% inclusive of crude fly ash, about 70% to about 85% inclusive of soil having a fineness modulus below 1.7, said soil comprising fine sand having substantially no binder content, at least 51% by weight of which passes a standard No. 40 sieve, and a maximum of 10% by weight of which passes a standard No. 200 sieve, the sum of the percentages of crude fly ash plus soil being substantially equal to 100, and about 2% to about 7% inclusive of lime, the percent lime being based on the weight of crude fly ash plush soil.

3. A stabilized soil composition of matter consisting essentially by weight of about 10% to about inclusive of crude fly ash, about 80% to about 90% inclusive of soil having a fineness modulus below 1.7, said soil comprising a granular material selected from the group consisting of gravel and sand containing a plastic component which is selected from the group consisting of clay and silt, a maximum of 35% by weight of soil passing a standard No. 200 sieve, and that portion of the soil which passes a standard No. 40 sieve having a maximum liquid limit of 40 and having a maximum plasticity index of 10, the sum of the percentages of crude fly ash plus soil being substantially equal to 100, and about 2% to about 7% inclusive of lime, the percent lime being based on the Weight of crude fly ash plus soil.

4. A stabilized soil composition of matter consisting essentially by weight of about 10% to about 20% inclusive of crude fly ash, about to about inclusive of soil having a fineness modulus below 1.7, said soil comprising a granular material selected from the group consisting of gravel and sand containing a plastic component which is selected from the group consisting of clay and silt, a maximum of 35% by weight of said soil passing a standard No. 200 sieve, that portion of said soil which passes a standard No. 40 sieve having a minimum liquid limit of 41 and having a maximum plasticity index of 10, the sum of the percentages of crude fly ash plus soil being substantially equal to 100, and about 2% to about 9% inclusive of lime, the percent lime being based on the weight of crude fly ash plus soil.

5. A stabilized soil composition of matter consisting essentially by weight of about 10% to about 20% inclusive of crude fly ash, about 80% to about 90% inclusive of soil selected from the group which consists of the silty and clayey soils having a fineness modulus below 1.7, at least 36% by weight of said soil passing a standard No. 200 sieve, the sum of the percentages of crude fly ash plus soil being substantially equal to 100, and about 3% to about 9% inclusive of lime, the percent lime being based on the weight of crude fly ash plus soil.

6. A stabilized soil composition of matter consisting essentially by weight of about 10% to about 20% inclusive of crude fly ash, about 80% to about 90% inclusive of soil selected from the group consisting of the clayey and silty soils having a fineness modulus below 1.7, that portion of said soil which passes a standard No. 40 sieve having a minimum plasticity index of 11, the sum of the percentages of crude fly ash plus soil being substantially equal to 100, and about 3% to about 9% inclusive of lime the percent lime being based on the weight of crude fly ash plus soil.

7. A stabilized compact load-supporting course for a road, highway or the like, characterized by strength sufiicient to support heavy loads and pliability suflicient for recompacting, consisting essentially of about 10% to 30% by weight inclusive of crude fly ash, about 70% to about 90% by weight inclusive of soil having a fineness modulus below 1.7, the sum of the percentages of crude fly ash plus soil being substantially equal to 100, about 2% to about 9% by weight inclusive of lime, the percent lime being based on the weight of crude fly ash plus soil, and about 5% to about 32% by weight inclusive of water, the percent water being based on the total weight of lime, fly ash and soil.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 254,342 Leidholdt Feb. 28, 1882 1,552,051 Crurne Sept. 1, 1925 1,886,933 Askenasy Nov. 8, 1932 1,942,769 Pefier et a1 Jan. 9, 1934 2,250,107 Nelles July 22, 1941 2,382,154 Jones et a1 Aug. 14, 1945 2,564,690 Havelin et al Aug. 21, 1951 

1. A STABILIZED SOIL COMPOSITION OF MATTER CONSISTING ESSENTIALLY BY WEIGHT OF ABOUT 10% TO ABOUT 30% INCLUSIVE OF CRUDE FLY ASH, ABOUT 70% TO ABOUT 90% INCLUSIVE OF SOIL HAVING A FINENESS MODULUS BELOW 1.7, THE SUM OF THE PERCENTAGES OF CRUDE FLY ASH PLUS SOIL BEING SUBSTANTIALLY EQUAL TO 100, AND ABOUT 2% TO ABOUT 9% INCLUSIVE OF LIME, THE PERCENT LIME BEING ON THE WEIGHT OF CRUDE FLY ASH PLUS SOIL. 